For me it's the Shimano XT M756A. I use 'em on my 29'er, same set for 4 years now with any issues (they're the older 756 version). It does take a little learning to adjust cup/cone hubs but once you do you can service these hubs for the cost of grease. I also run these hubs on my son's 26'ers and again, no issues for several years.